Hi Lee, can you please make a screenshot of the error you’re seeing? Also what mail service are you using? What version of eM client are you currently using?
Can you also go to Tools > Settings > Advanced and turn on SMTP logging for the problematic account?
- Save the settings
- Restart the application
- Replicate the issue
When the error occurs, go back to the advanced settings window and click on “Send Logs”, please send the logs to firstname.lastname@example.org and include a reference link to this forum topic.
Also are you using any firewall/proxy software on your computer or in your network?